(1) Field of the Invention
The present invention relates to a thermoplastic elastomer composition excellent in injection fusion bondability and surface gloss.
(2) Description of the Prior Art
An olefin type thermoplastic elastomer, for example, a partially crosslinked elastomer (TPE) comprising a crystalline polyolefin and an amorphous ethylene/.alpha.-olefin copolymer, shows an elastomeric property similar to that of a vulcanized rubber, and also shows a moldability equivalent to the moldability of a thermoplastic resin such as polyethylene or polypropylene. By utilizing these properties, the olefin type thermoplastic elastomer is molded in the same manner as ordinary resins, and molded article is used in the fields where the elastomeric property is required, for example, as a vehicle bumper, an exterior moleskin, a window shield gasket, an emblem, an interior surface sheet or a gasket for a construction material.
This TPE does not possess the surface gloss required in the market, and an improvement of the surface gloss has been desired especially for exterior moleskins and emblems of vehicles where great importance is attached to the surface gloss.
As means for offsetting the poor surface gloss of a shaped TPE article, there has been proposed a surface treatment such as a urethane coating. However, this treatment results in increase of the step number, and hence, it is desired to improve the surface gloss of the material per se without performing secondary processing.
An olefin type thermoplastic elastomer to be used for window shield gaskets of vehicles or various construction gaskets, for which properties similar to those of a vulcanized rubber are required, is obtained by increasing the content of an ethylene/.alpha.-olefin copolymer elastomer component in an ordinary olefin type thermoplastic elastomer.
The so-obtained thermoplastic elastomer rich in the softness is poor in the flowability in the fused state, and therefore, a window shield gasket for a vehicle or a construction gasket, for which a complicated shape is required, can hardly be prepared directly by injection molding of this thermoplastic elastomer.
Since this soft thermoplastic elastomer is excellent in profile moldability, there may be considered a method for forming the above molded article by extrusion molding. In this case, it is necessary to bond the ends of molded articles formed by profile extrusion.
This bonding is preferably accomplished according to a method in which at least two-extrusion-molded articles to be bonded are placed in a split mold and a thermoplastic elastomer having good fusion bondability is injected between the ends of the molded articles to fusion-bond the molded articles through the injected thermoplastic elastomer. In this case, it is preferred that the split mold should have a structure to which injection molding is applicable.
However, even if extrusion-molded articles of thermoplastic elastomers are bonded according to the above-mentioned method, in many cases, it is difficult to obtain bonding having a practical strength.